BUG #13685: Archiving while idle every archive_timeout with wal_level hot_standby

The following bug has been logged on the website:

Bug reference: 13685
Logged by: Laurence Rwoe
Email address: l(at)lrowe(dot)co(dot)uk
PostgreSQL version: 9.4.5
Operating system: Mac OS X 10.10
Description:

I'm seeing Postgres 9.4.5 archive while idle every archive_timeout when I
set ``wal_level hot_standby``:

$ initdb testpg
$ cat << 'EOF' >> testpg/postgresql.conf
> wal_level = hot_standby
> archive_mode = on
> archive_timeout = 10
> checkpoint_timeout = 1h
> archive_command = 'echo $(date) archive %p'
> log_checkpoints = on
> EOF
$ postgres -D testpg
LOG: database system was shut down at 2015-10-13 11:58:45 PDT
LOG: MultiXact member wraparound protections are now enabled
LOG: autovacuum launcher started
LOG: database system is ready to accept connections
Tue Oct 13 12:00:47 PDT 2015 archive pg_xlog/000000010000000000000001
Tue Oct 13 12:00:57 PDT 2015 archive pg_xlog/000000010000000000000002
LOG: checkpoint starting: xlog
Tue Oct 13 12:01:07 PDT 2015 archive pg_xlog/000000010000000000000003
LOG: checkpoint complete: wrote 0 buffers (0.0%); 0 transaction log file(s)
added, 0 removed, 0 recycled; write=0.000 s, sync=0.000 s, total=0.026 s;
sync files=0, longest=0.000 s, average=0.000 s
Tue Oct 13 12:01:17 PDT 2015 archive pg_xlog/000000010000000000000004
Tue Oct 13 12:01:27 PDT 2015 archive pg_xlog/000000010000000000000005
LOG: checkpoint starting: xlog
Tue Oct 13 12:01:38 PDT 2015 archive pg_xlog/000000010000000000000006
LOG: checkpoint complete: wrote 0 buffers (0.0%); 0 transaction log file(s)
added, 0 removed, 3 recycled; write=0.000 s, sync=0.000 s, total=0.027 s;
sync files=0, longest=0.000 s, average=0.000 s
Tue Oct 13 12:01:48 PDT 2015 archive pg_xlog/000000010000000000000007
Tue Oct 13 12:01:58 PDT 2015 archive pg_xlog/000000010000000000000008
LOG: checkpoint starting: xlog
LOG: checkpoint complete: wrote 0 buffers (0.0%); 0 transaction log file(s)
added, 0 removed, 3 recycled; write=0.000 s, sync=0.000 s, total=0.001 s;
sync files=0, longest=0.000 s, average=0.000 s

At ``wal_level archive`` I only see archiving every checkpoint_timeout (that
it archives every checkpoint_timeout is a known limitation, see
http://www.postgresql.org/message-id/1407389876762-5813999.post@n5.nabble.com):

$ initdb testpg
$ cat << 'EOF' >> testpg/postgresql.conf
> wal_level = archive
> archive_mode = on
> archive_timeout = 10
> checkpoint_timeout = 60
> archive_command = 'echo $(date) archive %p'
> log_checkpoints = on
> EOF
# lrowe(at)Laurences-iMac ~/scratch
$ postgres -D testpg
LOG: database system was shut down at 2015-10-13 12:25:38 PDT
LOG: MultiXact member wraparound protections are now enabled
LOG: autovacuum launcher started
LOG: database system is ready to accept connections
Tue Oct 13 12:25:49 PDT 2015 archive pg_xlog/000000010000000000000001
LOG: checkpoint starting: time
LOG: checkpoint complete: wrote 0 buffers (0.0%); 0 transaction log file(s)
added, 0 removed, 0 recycled; write=0.000 s, sync=0.000 s, total=0.029 s;
sync files=0, longest=0.000 s, average=0.000 s
Tue Oct 13 12:26:39 PDT 2015 archive pg_xlog/000000010000000000000002
LOG: checkpoint starting: time
LOG: checkpoint complete: wrote 0 buffers (0.0%); 0 transaction log file(s)
added, 0 removed, 1 recycled; write=0.000 s, sync=0.000 s, total=0.030 s;
sync files=0, longest=0.000 s, average=0.000 s
Tue Oct 13 12:27:39 PDT 2015 archive pg_xlog/000000010000000000000003

I think this additional archiving at wal_level hot_standby is a bug.